We studied the presence and morphology of plaque-like lesions in the frontal cortex of six patients, aged 40 to 76 years, with hereditary cerebral hemorrhage with amyloidosis--Dutch type (HCHWA-D), using beta/A4 immuno-, silver, Congo red and thioflavin S staining. Two types of beta/A4 immunoreactive and Congo red-negative plaques were detected. The first type was composed of argyrophilic fibrous material in periodic acid-methenamine silver (PAM) and modified Bielschowsky staining and lacked silver-stained degenerating neurites. Therefore, this type of plaque has the same staining properties as the diffuse plaque described in Alzheimer's disease, Down's syndrome and nondemented elderly. The second type of plaque, occurring only in the three oldest patients and numerically increasing with age, consisted of a spherical non-argyrophilic area of granular texture with a rim of PAM-positive material. The PAM-positive fibrous material of both types of plaques was mingled with coarser and compact, irregular-shaped argyrophilic structures in the oldest patient. The described plaques did not show bright fluorescence with thioflavin S staining. These results indicate, that the morphology of plaques, encountered in HCHWA-D, is diverse and changes with age.